Active flow control applied to an airfoil

Donovan, John; Krai, Linda D.; Gary, Andrew W.

doi:10.2514/6.1998-210

Cited by 116 publications

(74 citation statements)

References 13 publications

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“…Using an appropriate combination of frequency ( F + ≈ 1) and magnitude (< > c µ = 10 to 50x10 -5 ) the flow should be steadier, even if it is intermittently separated. Similar trends, at least for the lift increment and the excitation F + , were identified numerically 6 . Oscillatory addition of momentum is two orders of magnitude more efficient than tangential steady blowing for separation control 2,4 .…”

supporting

confidence: 58%

“…Low Reynolds number experiments, where control was applied from the LE region of the airfoils, were repeated at a chord Reynolds number of 37.6x10 6 . Using a flapped NACA 0015 airfoil, where control was applied at the flap shoulder, it was shown that the method is essentially independent of Reynolds number 4 , as long as the appropriate dimensionless control parameters are applied.…”

mentioning

confidence: 99%

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Oscillatory excitation of unsteady compressible flows over airfoils at flight Reynolds numbers

Seifert

Pack

1999

37th Aerospace Sciences Meeting and Exhibit

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An experimental investigation, aimed at delaying flow separation due to the occurrence of a shock-waveboundary-layer interaction, is reported. The experiment was performed using a NACA 0012 airfoil and a NACA 0015 airfoil at high Reynolds number incompressible and compressible flow conditions. The effects of Mach and Reynolds numbers were identified, using the capabilities of the cryogenic-pressurized facility to maintain one parameter fixed and change the other. Significant Reynolds number effects were identified in the baseline compressible flow conditions even at Reynolds number of 10 and 20 million. The main objectives of the experiment were to study the effects of periodic excitation on airfoil drag-divergence and to alleviate the severe unsteadiness associated with shock-induced separation (known as "buffeting"). Zero-mass-flux oscillatory blowing was introduced through a downstream directed slot located at 10% chord on the upper surface of the NACA 0015 airfoil. The effective frequencies generated 2-4 vortices over the separated region, regardless of the Mach number. Even though the excitation was introduced upstream of the shock-wave, due to experimental limitations, it had pronounced effects downstream of it. Wake deficit (associated with drag) and unsteadiness (associated with buffeting) were significantly reduced. The spectral content of the wake pressure fluctuations indicates of steadier flow throughout the frequency range when excitation was applied. This is especially important at low frequencies which are more likely to interact with the airframe. have shown that periodic vortical excitation introduced into a separating boundary layer, slightly upstream of the average separation location, can effectively delay boundary layer separation. The improved ability of the boundary layer to overcome an adverse pressure gradient is attributed to enhanced mixing between the low momentum fluid near the wall and the external high momentum flow. The successful application of the method increases the lift while maintaining low drag. At low Mach numbers, where high-lift for take-off, landing or loiter is required, the delay of boundary layer separation allows increased loading of a multi-element high-lift airfoil system.It was recently demonstrated 4 that periodic excitation of the boundary layer upstream of separation can delay the occurrence of the adverse effects associated with boundary layer separation and significantly enhance the performance of airfoils at flight Reynolds numbers and incompressible speeds. Low Reynolds number experiments, where control was applied from the LE region of the airfoils, were repeated at a chord Reynolds number of 37.6x10 6 . Using a flapped NACA 0015 airfoil, where control was applied at the flap shoulder, it was shown that the method is essentially independent of Reynolds number 4 , as long as the appropriate dimensionless control parameters are applied.A recently published numerical simulation 5 shows that oscillatory excitation of a separated boundary layer, at ...

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supporting

confidence: 58%

mentioning

confidence: 99%

Oscillatory excitation of unsteady compressible flows over airfoils at flight Reynolds numbers

Seifert

Pack

1999

37th Aerospace Sciences Meeting and Exhibit

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“…Different spatial profiles of V A (x) over the orifice have been considered. Numerical experiments [2,3] (within the scope of their model) indicate that a "top-hat" distribution most closely matches the experimental data. A modified boundary condition on the pressure at the orifice is introduced through a consideration of the normal momentum equation.…”

Section: Introductionmentioning

confidence: 75%

“…In the work of Kral et al [2] and Donovan, Kral, and Cary [3], the flow within the cavity is not calculated and the perturbation to the flowfield is introduced through the wall-normal component of velocity at the orifice exit…”

Section: Introductionmentioning

confidence: 99%

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Reduced-Order Model for Efficient Simulation of Synthetic Jet Actuators

2005

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The application of passive air jet vortex-generators to stall suppression on wind turbine blades

2016

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An experimental study was performed to assess the feasibility of passive air jet vortex-generators to the performance enhancement of a domestic scale wind turbine. It has been demonstrated that these simple devices, properly designed and implemented, can provide worthwhile performance benefits for domestic wind turbines of the type investigated in this study.In particular, this study shows that they can increase the maximum output power coefficient, reduce the cut-in wind speed and improve power output at lower wind speeds while reducing the sensitivity to wind speed unsteadiness. A theoretical performance analysis of a 500 kW stall-regulated wind turbine, based on blade element momentum theory, indicates that passive air jet vortex-generators would be capable of recovering some of the power loss because of blade stall, thereby allowing attainment of rated power output at slightly lower average wind speeds.

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Active flow control applied to an airfoil

Cited by 116 publications

References 13 publications

Oscillatory excitation of unsteady compressible flows over airfoils at flight Reynolds numbers

Oscillatory excitation of unsteady compressible flows over airfoils at flight Reynolds numbers

Reduced-Order Model for Efficient Simulation of Synthetic Jet Actuators

The application of passive air jet vortex-generators to stall suppression on wind turbine blades

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